Keyboard type electronic musical instrument



MASUBMCSMURAD ETAL Nov. 10, 1970' KEYBOARD TYPE ELECTRONIC MUSICALINSTRUMENT 3 Sheets-Sheet 1 Original Filed Jan. 25, 1965 FIG.

Ma mm m E M mm 1 R 0 M5 m 0 M Nov. 10, 1970 MASUO oMuRA El'AL KEYBOARDTYPE ELECTRONIC MUSICAL INSTRUMENT briginal Filed Jan. 25. 1965 2 SIGNAL577 501/205 PRIOR ART 2// S/G/VAL 50/1205 20/ 20 56 203 S/GNAL/VO/VL/NEAR LOW-PASS SOURCE CIRCUIT /L 208 SIG/VAL SOURCE 20/ 2/3 FIG. 4

, SIGNAL SOURCE S/GNAL SOURCE 5 Sheets-Shet 2 MT M ey:

NOV. 10, M'ASUQ OMURA ETAL KEYBOARD TYPE ELECTRONIC MUSICAL INSTRUMENTCriginal Filed Jan. 25, 196s 3 Sheets-Sheet 3 INVENTORS M19510 Mum? IIIBSHHMD TQM w 1 United States Patent. Office 3,539,698 Patented Nov.10, 1970 US. Cl. 841.11 11 Claims ABSTRACT OF THE DISCLOSURE Anelectronic musical instrument of keyboard type which has (1) a signalgenerating system composed of twelve tone series of signal sources forgenerating signals of pitches corresponding to the equal temperedmusical scale, (2) a keyswitch system for switching tone signals to anoutput system by depressed keys on a keyboard, (3) the output systemwhich converts them to acoustic tones, and (4) a difference-signalsystem which is included in the signal generating system and whichcomprises nineteen ditference-signal generators for producing nineteendifference-signals in a low frequency range in such a way that (a) eachof lower seven series of the twelve tone series has a pair ofdifference-signal generators, one of which produces a difference-signalas the lowest signal of each of lower seven series, and the other ofwhich produces a difference-signal as the second lowest signal of eachof lower seven series, (b) each of upper five series of the twelve toneseries has a single differencesignal generator which produces adifference-signal as the lowest signal of each of upper five series, and(c) each of nineteen difference-signal generators mixes two signals ofsignal sources, one signal in octave relation and the other signal innon-octave relation to a differencesignal to be produced by adifference-signal generator.

CROSS-REFERENCE TO RELATED APPLICATIONS This application is acontinuation of our US. application Ser. No. 427,621 filed Jan. 25,1965, now abandoned.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates generally to an electronic musical instrument of keyboard type,and more particularly to an electronic musical instrument having, inaddition to normal signals for producing musical tone signals, two kindsof difference-signals, one of which is made by mixing two signals in apitch interval of musical perfect fifth, i.e., two signals in frequencyratio of about 2:3, the other of which is made by mixing two signals ina pitch interval of musical perfect fourth, i.e., two signals infrequency ratio of about 3:4. Each of said two kinds ofdifference-signals has a frequency of the difference between twofrequencies of said two signals. (The pitch intervals of musical perfectfifth and musical perfect fourth are defined in the musicalterminology.)

DESCRIPTION OF THE PRIOR ART In a conventional electronic musicalinstrument of keyboard type, one kind of difference-signal has beenused. Such kind of difference-signal is made by mixing two signals in apitch interval of musical perfect fifth, i.e., in frequency ratio of2:3. This kind of differencesignal will be hereinafter referred to, forconvenience, as a perfect fifth type difference-signal. Since theperfect fifth type difference-signal is lower in pitch by one octavethan the lower one of the two mixed signals, such perfect fifth typedifference-signal is only used as the lowest signal of each of twelvetone series of tone signals, i.e., C, Cit, D, Dii, E, F, Ft, G, Git, A,At and B tone series of tone signals.

The nonlinearity of amplifiers, speakers, human ears or nonlinearcircuits is responsible for producing a difference-signal having adifference frequency between two frequencies of two signals. In view ofsuch a fact, a certain kind of conventional pipe organ has partly hadthe perfect fifth type difference tones (signals) as tones of the pedalkeyboard, and a certain kind of conventional electronic organ has alsohad the perfect fifth type difference-signals as tone signals of thepedal keyboard.

These conventional difference signals are of turbid tone color anddifferent in tone color from the normal signals derived directly fromsignal sources such as oscillators and frequency divider circuits.Therefore, the conventional difference signals have been only used astone signals of the pedal keyboard but not used as tone signals of themanual keyboard.

SUMMARY OF THE INVENTION An object of the invention is to provide anelectronic musical instrument characterized by a tone signal generatingsystem for generating signals which include normal signals and two kindsof difference-signals, each of said signals having an individual pitchdifferent from each other.

Another object of the invention is to provide a difference-signalgenerator for producing a novel differencesignal which has nodisadvantage of producing turbid tone color and which is similar, intone color, to the normal signal.

A further object of the invention is to provide difference-signals whichare of a desirable tone color and are used satisfactorily as tonesignals of the manual keyboard.

The invention will be obvious from the following detailed descriptionwith reference to the acocmpanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a basic circuit diagram of atone signal generating system which produces normal signals and twokinds of difference signals in accordance with the invention;

FIG. 2 is an electrical diagram of means for generating a conventionaldifference-signal;

FIG. 3 and FIG. 4 are electrical circuits according to the inventioncapable of eliminating the turbid and undesirable tone color of theconventional differencesignal;

FIG. 5 is a circuit diagram of a nonlinear circuit for producing adifference-signal; and

FIG. 6 is a basic circuit diagram of a modified embodiment of a tonesignal generating system in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before going into a detaileddescription, it is pointed out that the explanation set forthhereinafter will be simplified as much as possible to provide an easyunderstanding of the embodiments and the scope of the invention. Thenumber of signal sources, keyswitches and resistors, etc. will begreatly reduced by way of explanation. As the practical matter, ofcourse, the number of different kinds of tones should be at least twelveso as to ensure a complete musical scale comprising musical tones C,Cit, D Dii, E, F, Fit, G, Git, A, All and B. Although the explanationset forth hereinafter will be limited to certain characteristic parts ofan electronic musical instrument in accordance with the inven tion, theother parts will be easily understood therefrom Referring to FIG. 1,normal signal sources 101 to 119 necessary for a conventional signalgenerating system are shown for easy understanding of the presentinvention. Normal signals are generated by normal signal sources 190,191, 192 198 199 such as oscillators and frequency dividers and twokinds of difference-signals are generated by two kinds ofdifferencesignal generators 271 to 277, as a first kind, and 278 to 289,as a second kind. Each of the first kind of difference-signal generators271 to 277 generates a differencesignal by mixing two signals in'a pitchinterval of musical perfect fourth, i.e., two signals in frequency ratioof about 3:4. Each of the second kind of difference-signal generators278 to 289 generates a difference-signal by mixing two signals in apitch interval of musical perfect fifth, i.e. in frequency ratio ofabout 2:3. In such an arrangement, according to the invention, there isno need to employ the normal signal sources 101 to 119 for generatingnineteen normal signals of musical scale in a low frequency range.According to the tone signal generating system of the invention,nineteen tone signals of the musical scale in a low frequency range aremade of nineteen difference-signals produced by the two kinds ofdifference-signal generators 271 to 277 and 278 to 289.

In the detailed description to be made hereinafter, the tonescorresponding to the musical scale are designated in order of pitch fromthe lowest tone as follows; C 1 D1 1 1, 1, i 1 1 1, 1 1 2, C tt, D ...BC ...B C ...B C C Signal sources 190, 191, 192, 193, 194, 195, 196, 197,198 and 199 generate signals of G it, G A C C it, D D ti, F t, G and CAtones, respectively, and are tuned in accordance with the equaltemperatment.

In the C-series of tone signals C C C two kinds of difference-signalgenerators 271 and 283 are employed without using the two signal sources101 and 113. The difference-signal generator 271 produces adifference-signal of C by mixing the two signals G (196.0 Hz.) and 0(261.7 Hz.) derived from the signal sources 190 and 193 in a pitchinterval of perfect fourth, i.e., in frequency ratio of about 3:4,through resistors 238 and 239, respectively. The difference-signal of C(65.7 Hz.) successively enters a keyswitch 220. The otherdifferencesignal generator 283 produces a difference-signal of C bymixing the two signals C (261.7 Hz.) and 6, (392.0 Hz.) derived from thesignal sources 193 and 198 in a pitch interval of perfect fifth, i.e.,in frequency ratio of about 2:3, through resistors 250 and 251,respectively. The difference-signal of C (130.3 Hz.) successively entersa keyswitch 226.

The former type difference-signal will hereinafter be referred to, forconvenience, as a perfect fourth type difference-signal. Since theperfect fourth type differencesignal C is lower in pitch -by one and ahalf octave than the lower signal G of the two mixed signals G and C ofthe signal sources 190 and 193, the perfect fourth typedifference-signal C is used as the lowest signal of the C-series ofsignals. The difference-signal C which will hereinafter be referred toas a perfect fifth type difference-signal, is lower in pitch by oneoctave than the lower signal C of the two mixed signals C and G of thesignal sources 193 and 198, and is used as the second lowest signal ofthe C-series. Therefore, there is no need to use the lowest two signalsources 101 and 113 of C-series of normal signal sources 101, 113, 193 Asignal C generated by the signal sources 193 is fed to a keyswitch 231through a resistor 257 so as to form the tone signal C Higher tonesignals 0,, C (not shown) of C-series are formed in the same way as thatof the tone signal C Thus all C-series tone signals are completed.

Similarly, also for tone signals of Cit-series, D-series, Dir-seriesE-series and F-series, two kinds of differencesignal generators areemployed in each series, without using the lowest two signal sources.

In the Flt-series of tone signals F t, F 11, F 1? two kinds ofdifference-signal generators 277 and 289 are also employed, similarly tothe C-series, Cit-series, D-series, Dit-series, E-series and F-series,without using the lowest two signal sources 107 and 119. Thedifference-signal generator 277 produces a difference-signal of F t bymixing two signals C 1? (277.2 HZ.) and F il (370.0 Hz.) derived fromthe signal sources 194 and 197 in a pitch interval of perfect fourththrough resistors 244 and 245, respectively. The difference-signal of Ft (92.8 Hz.) enters a keyswitch 223. The other difference-signalgenerator 289 produces a difference-signal of F 1? by mixing two signalsF 1 (370.0 Hz.) and 1 i (554.4 Hz.) derived from the signal sources 197and 199 in a pitch interval of perfect fifth through resistors 252 and253, respectively. The differencesignal of P 1? (184.4 Hz.) enters akeyswitch 227. The signal F 13 generated by the signal sources 197 isfed to a keyswitch 235 through resistor 261 so as to form a tone signalF tl. Higher tone signals Fgt, F 1? (not shown) of Fit-series are formedin the same way as that of the tone signal F it. Thus, all Fit-seriestone signals are completed.

Therefore, for tone signals of the lower seven series, namely theC-series, Cit-series, D-series, Dii-series, E- series, F-series andFit-series, a pair of difference-signal generators, i.e., a perfectfourth type difference-signal generator and a perfect fifth typedifference-signal generator are employed in each series without usingthe lowest two signal sources of said each series. Fourteen signalsources 101 to 107 and 113 to 119 of the lower seven series are saved byusing seven perfect fourth type difference-signal generators 271 to 277and seven perfect fifth type difference-signal generators 2 83 to 289.

In the G-series tone signals, G G G one kind of difference-signalgenerator 278 is employed without using the lowest signal source 108 ofthe G-series. The difference-signal generator 278 produces a differencesignal of G, by mixing two signals G (196.0 Hz.) and D, (293.7 Hz.)derived from the signal sources and in a pitch interval of perfect fifththrough resistors 246 and 247, respectively. The difference-signal of G(97.7 Hz.) successively enters a keyswitch 224. The signal G generatedby the signal source 190 is fed to a keyswitch 228 through resistor 254so as to form a tone signal G The signal G generated by the signalsource 198 is fed to a keyswitch 236 through resistor 262 so as to forma tone signal G Higher tone signals G G (not shown) of the G-series areformed in the same way as those of the tone signals G and G Thus, allG-series tone signals are completed.

Similarly, for tone signals of the Git-series, A-series, Ait-series, andB-series, one kind of difference signal generator is employed in eachseries without using the lowest signal source.

Therefore, for tone signals of the upper five series, namely G-series,Git-series, A-series, Aii-series and B- series, a singledifferent-signal generator, i.e., a perfect fifth type difference-signalgenerator, is employed in each series without using the lowest signalsource of each series. Five signal sources 108 to 112 of the upper fiveseries are saved by employing five perfect fifth type difference-signalgenerators 278 to 282 (not shown).

A perfect fourth type difference-signal generator may be substituted fora perfect fifth type difference-signal generator. That is to say, forexample, the difference signal G is produced either by the perfect fifthtype difference-signal generator 278 having two signals G (196.0 Hz.)and D (293.7 Hz.) of the signal sources 190 and 195 mixed togethertherein or by a perfect fourth type difference-signal generator in whichtwo signals D (293.7 Hz.) and G (392.0 Hz.) of the signal sources 195and 198 may be mixed together, because the signal 6;, of the signalsource 19 8 exists actually in the signal generating system of FIG. 1.On the other hand, for example, the difierence signal C can be producedby the perfect fourth type difference-signal generator 271 having twosignals G 196.0 Hz.) and C (261.7 Hz.) of the signal sources 190 and 193mixed together therein, but can not be produced by a perfect fifth typedifferencesignal generator in which two signals C (130.8 Hz.) and G(196.0 Hz.) of the signal sources 113 and 190 would have been mixedtogether, because the signal C (130.8 Hz.) of the signal source 113 doesnot exist actually in the signal generating system of FIG. 1.

Consequently, for twelve series of signal sources, nineteen signalsources 101, 102, 103 118 and 119 are saved by using nineteendifference-signal generators 271, 272, 273 289 in a low frequency range.The nineteen difference-signal generators act as nineteen signal sourcessuch as oscillators and frequency dividers.

Tone signals C C 11, D derived from respective keyswitches 220, 221, 222are fed to an output system (not shown), where the tone signals areamplified by an amplifier (not shown) and converted into acoustic tonesby electro-ace-ustic translating means (not shown) such as a spealter.

According to the principle of the invention as explained with referenceto FIG. 1, for example, in an electronic musical instrument havingsixty-one keys on the manual keyboard thereof, sixty-one tone signalscan be composed partly of forty-two normal signals generated directly byforty-two signal sources in a high frequency range and partly ofnineteen difference-signals generated indirectly by nineteen pairs ofsignals of the forty-two signal sources through nineteendifference-signal generators. Therefore, the forty-two signal sourcesgenerate sixty-one tone signals by using the nineteen difference-signalgenerators as shown in FIG. 1. It will be easily understood that thedifference-signal system of FIG. 1 is effectively applicable also to anelectronic musical instrument having two or more manual keyboards.

In general, a conventional tone signal generating system comprisesoscillators and frequency dividers. The frequency dividers usuallyemploy flip-flop circuits, each of which has two transistors or twovacuum tubes. According to the principle of the invention, therefore,nineteen frequency dividers are replaced by the difference-signal systemwhich comprises the nineteen difference-signal generators. That is tosay, thirty-eight transistors or thirtyeight vacuum tubes are saved byvirtue of the differencesignal system. Thus, the principle of theinvention makes it possible to construct an electronic musicalinstrument at low cost by employing the difference signal system.

When the pitches of the difference-signals described hereinbefore arecompared with the pitches of signals which would have been obtaineddirectly from the signal sources tuned in accordance with the equaltempered musical scale, each pitch of the difference-signals deviatesvery slightly from each pitch of the signals corresponding to the equaltempered musical scale. For example, 65.7 Hz. and 97.7 Hz. of thedifference-signals C and G respectively, deviate very slightly from 65.4HZ. and 98.0 Hz. of the tone signals C and G corresponding to the equaltemperament. But the deviated difference-signals can be applied, withouthindrance, to the tone sign al generator system of the electronicmusical instrument according to the invention.

The following description with reference to FIGS. 2, 3, 4 and 5 willexplain the details of each difference-signal generator shown in FIG. 1.

Referring to FIG. 2, as an example, a signal source 201 generates asignal having a frequency of 3n Hz.

and a signal source 202 generates a signal having a frequency of Zn Hz.A signal at a frequency of 3n Hz. and a signal at a frequency of Zn Hz.are fed to an output terminal 212 through resistors 210 and 211,respectively, so as to form a mixed signal. The mixed signal derivedfrom the output terminal 212 is converted by nonlinearity, such asnonlinearity of amplifiers, speakers, human ears or nonlinear circuits,into a difference-signal of a difference-frequency n Hz. which is thedifference frequency between 3n Hz. of the signal of the signal source201 and Zn Hz. of the signal of the signal source 202.

When these signal source 201 and 202 are precisely tuned according tothe equal temperament, the frequency of the signal generated by thesignal source 202 is 2n Hz. (for example, G 196.0 Hz.=2 98.0 Hz.), butthe frequency of the signal generated by the signal source 201 is 3n Hz.(for example, D 293.7 HZ.=3 97.9 HZ.) which is slightly lower than 3nHz. (for example, 3 98.0 Hz.) In other words, the frequency 3n deviatesslightly from an exact frequency 3n. Therefore, the signal having 3n hasharmonics 3n, 6n, 9n, 12n' while the signal having 2n has harmonics 2n,4n, 6n, 8n

For convenience, the frequency n'(for example, 97.9 Hz.) is defined tobe smaller by a very little frequency An (for example, 0.1 Hz.) than thefrequency n (for example, 98.0 Hz.), namely n'=nAn.

Harmonics of the difference signal are produced by the harmonics of thetwo signals, namely 3n, 6n, 9n, and Zn, 4n, 6n, 8n so that the harmonicsof the difference signal include difference frequency componentsn"(=3n'2n), 2n"( =6n'4n), 3n(=9n' 6n), 4n(=12n8n) The frequency n"'issmaller by 3An than n, namely n"=n3An, because 3n'=3(nAn), n"=3(nA)n2n=n3An.

Considering these harmonics and difference frequency components,therefore, the frequency spectrum of the difference signal isconstituted by n", (2n, 2n), (3n, 3n), (4n, 4n), (512), (6n, 6n, 6n") Adifference signal having such a complicated frequency spectrum isgreatly different in tone color from a signal having a simple frequencyspectrum of 11, Zn, 3n, 4n, 5n, 6n which would have been deriveddirectly from a signal source. Frequency components 2n", (3n, 3n), 4n",5n", (6n, 6n") which are slightly deviated from harmonics 2n, 3n, 4n,5n, 6n make the difference signal of turbid and undesirable tone color.This is the reason why tone signals except pedal tone signals have notbeen composed of conventional difference signals. Pedal tone signals maybe different in tone color from tone signals of manual keyboards. Pedaltone signals are usually careless about a turbid tone color.

Referring to FIG. 3, signal sources 201 and 202 are tuned according tothe equal temperament, and, as an example, the signal source 201generates a signal having a frequency of Sn and the signal source 202generates a signal having a frequency of Zn. Consequently, the signalgenerated by the signal source 201 has a frequency spectrum of 3n, 6n,9n, 12n and the signal generated by the signal source 202 has afrequency spectrum of Zn, 4n,6n,8n

These two signals are mixed and fed to a nonlinear circuit 205 throughresistors 203 and 204, respectively, so as to form a difference signal.The difference signal derived from the nonlinear circuit 205 hasfrequency components n", (2n, 2n), (3n, 3n"), (4n, 4n"), (5n"), (6n, 6n,6n) and is fed to a low pass filter 206 to weaken or eliminate overtonefrequency components (2n, 2n"), (3n, 3n), (4n, 4n"), (5n"), (6n, 6n,6n") Thus, the difference signal derived from the low pass filter 206has the lowest frequency component n" of a relatively large amplitude,and the overtone frequency compontnts (2n, 2n"), (3n, 3n"), (4n, 4n"),(5n"), (6n, 6n, 6n") are substantially removed.

The difference signal derived from the low pass filter 206 and thesignal generated by the signal source 202 are fed to an output terminal209 through resistors 207 and 208, respectively. Thus, a noveldifference signal is obtained by a novel difference signal generatoraccording to the invention. The difference signal generator produces anovel difference signal having a frequency spectrum n, 2n, 4n, 6n, 8n

As a result, the novel difference signal produced by the noveldifference signal generator including a low pass filter does not have aturbid and undesirable tone color, but has a natural tone color similarto a tone color of a signal which would have been generated directly bya signal source.

Referring to FIG. 4, two signals generated by signal sources 201 and 202are the same as the two signals described with reference to FIG. 3.

The signal generated by the signal source 201 has frequency components3n, 611, 911, and is fed to a low pass filter 213 to weaken or eliminateovertone frequency component 6n, 9n, l2n Thus, the signal derived fromthe low pass filter 213 has the lowest component 3n of a relativelylarge amplitude, and the overtone frequency components 6n, 9n, l2n aresubstantially removed.

The signal derived from the low pass filter 213 has almost only thelowest frequency component 3n, while the signal generated by the signalsource 202 has frequency components 2n, 4n, 6n, 8n These two signals arefed to an output terminal 216 through resistors 214 and 215,respectively, so as to form a mixed signal.

The mixed signal derived from the output terminal 216 is converted bynonlinearity, such as nonlinearity of a nonlinear circuit, into adifference signal of a difference frequency n which is the differencebetween 311' corresponding to the frequency component of the signalderived from the low pass filter 213 and 211 corresponding to the lowestfrequency component of the signal generated by the signal source 202.Thus, another novel difference signal is obtained, and anotherdifference signal generator is made according to the invention. Saidanother difference signal generator produces another novel differencesignal in a frequency spectrum of n", Zn, 311', 4n which is similar to anormal frequency spectrum n, 2n, 3n, 4n As a result, the differencesignal produced by said another difference signal generator including alow pass filter does not have a turbid and undesirable tone color buthas a desired and naturaltone color.

The above description with reference to FIG. 3 and FIG. 4, has explainedabout novel difference signals, and has explained, as an example, anovel perfect fifth type difference-signal which is produced by mixingtwo signals in a pitch interval of perfect fifth, i.e., in frequencyratio of 2n23n'. One of the two signals has an exact frequency 2n, whichis essentially in octave relation to the frequency of the differencesignal; while, the other of the two signals has a slightly deviatedfrequency 3n which is in nonoctave relation to the frequency of thedifference signal. It is easily understood that another kind of noveldifference-signal can be obtained by mixing two signals in a forachieving said other kind of novel difference-signal, i.e.,

the novel perfect fourth type difference-signal that the signal source201 generates a signal having a slightly deviated frequency 3n and thesignal source 202 generates a signal having an exact frequency 411 withreference to the low 8 pass filter type difference signal generatorshown in FIG. 3 or FIG. 4.

Since the low pass filter type difference signal generators can not onfybe employed as perfect fifth type differencesignal generators, but alsobe employed as perfect fourth type difference-signal generators, the lowpass filter type difference-signal generators can be used as nineteendifference-signal generators mentioned with respect to FIG. 1.Therefore, successive tone sginals of the manual keyboard can becomposed partly of novel difference-signals and partly of signals ofsignal sources. The successive tone signals are much alike in tonecolor.

Referring to FIG. 5, two signals in a pitch interval of perfect fourthor perfect fifth are mixed and fed together, through resistors 421 and42-2, to a circuit comprising a parallel connection of resistor 423, adiode 424 and a capacitor 425 grounded at one end thereof and areconverted into a difference-signal having an intensified fundamentalpitch thereof. The difference-signal is derived through a resistor 428.The circuit is used as a nonlinear circuit adapted for thedifference-signal generators as shown in FIGS. 1, 3 and 4.

Referring to FIG. 6, a generator system 301 includes signal sources 280,281, 282 299 and 300, and a keyswitch system 302 of a manual keyboardincludes keyswitches 303, 304, 305, 306, 307 and 308 which correspond totone signals G f, G F tl, G F t and C respectively.

The pitch of the tone signal C corresponding to the keyswitch 308 isdetermined by a perfect fourth type difference signal derived, through aresistor 358, from a perfect fourth type difference-signal generator 370in which two signals G and C generated by signal sources 293 and 280 ina pitch interval of perfect fourth are mixed together through resistors360 and 359, respectively.

The perfect fourth type difference-signal C is mixed with fiveadditional signals, which are essentially in octave relation to saidperfect fourth type difference-signal C and four of which are signals CC C and C derived, through resistors 354, 353, 352 and 351, from thesignal sources 280, 281, 282 and 283, respectively, and the remainingone of which is a perfect fifth type differencesignal corresponding to Cderived, through a resistor 355, from a perfect fifth typedifference-signal generator 371 in which two signals C and G generatedby the signal sources 280 and 294 in a pitch interval of perfect fifthare mixed together through resistors 356 and 357, respectively, so thatthe tone signal C becomes rich in tone color.

Tone signals C it, D D t, E and F (not shown) are composed of signalshaving the same relationship as that of the signals associated with thetone signal C Similarly, the pitch of the tone signal F it correspondingto the keyswitch 307 is determined by a perfect fourth typedifference-signal derived, through a resistor 348, from a perfect fourthtype difference-signal generator 372 in which two signals 0 1$ and F 1?generated by the signal sources 284 and 290 in a pitch interval ofperfect fourth are mixed together through resistors 350 and 349, respectively. The perfect fourth type difference-signal F t is mixed with fouradditional signals, which are essentially in octave relation to saidperfect fourth type differencesignal F t, and three of which are signalsF f, E f and F il derived, through resistors 344, 343 and 342, from thesignal sources 290, 291 and 292, respectively, and the remaining one ofwhich is a perfect fifth type difference-signal corresponding to F itderived, through a resistor 345, from a perfect fifth typedifference-signal generator 374 in which two signals F ll and C 1?generated by the signal sources 290 and 285 in a pitch interval ofperfect fifth are mixed together through resistors 333 and 334,respectively, so that the tone signal F 1? becomes rich in tone color.

Each of the seven tone signals mentioned above, i.e.,

the tone signals C C f, D DJ, E, F and Fit is composed of a perfectfourth type difference-signal and of several additional signalsincluding signals from signal sources and a perfect fifth typedifference signal, the several additional signals being essentially inoctave relation to said perfect fourth type difference-signal and actingas upper harmonics of said perfect fourth type differencesignal.

A pitch of the tone signal G corresponding to the keyswitch 306 isdecided by a perfect fifth type differencesignal derived, through aresistor 339, from a perfect fifth type difference-signal generator 373in which two signals G and D generated by the signal sources 293 and 287in a pitch interval of perfect fifth are mixed together throughresistors 340 and 341, respectively. The perfect fifth typedifference-signal G is mixed with four additional signals G G G and Gderived, through resistors 338, 337, 336 and 335, from the signalsources 293, 294 295 and 296, respectively, so that the tone signal Gbecomes rich in tone color.

T0116 signals C1112, A1, A li, B1, C2, Cgli, D2, Dzii, E2 and F (notshown) are composed of signals having the same relationship as that ofthe signals concerning the tone signal G Similarly, a pitch of the tonesignal F il corresponding to the keyswitch 305 is decided by a perfectfifth type difference-signal derived, through a resistor 3-32, fromaforesaid perfect fifth type difference-signal generator 374. Theperfect fifth type difference-signal generator 374 is commonly used forthe tone signals F 1? and F fi. The perfect fifth type difference-signalP 3; is mixed with three additional signals F ii, F 1? and F 1? derived,through resistors 331, 330 and 329, from the signal sources 290, 291 and292, respectively, so that the tone signal F 1? becomes rich in tonecolor.

Each of the twelve tone signals mentioned above, i.e., the tone signalsG1, 611*, A1, A li, B1, C2, czli, D2, Dzli, F and P 1; is composed of aperfect fifth type differencesignal and of several additional signals ofsignal sources, the several additional signals being essentially inoctave relation to said perfect fifth type difference-signal and actingas upper harmonics of said perfect fifth type difference-signal.

As a practical matter, each of these difference signal generators 370,371, 372 is replaced with the low pass filter type difference-signalgenerator as shown in FIG. 3 or FIG. 4. The low pass filter typedifferencesignal generator has a nonlinear circuit such as the circuitcomprising a parallel connection of resistor 423, diode 424 andcapacitor 425 shown in FIG. 5.

A pitch of the tone signal G corresponding to the key switch 304 isdetermined by the signal G derived from the signal source 293 through aresistor 328. The signal G is mixed with three additional signals G Gand G derived from the signal sources 294, 295 and 296 through resistors327, 326 and 325, respectively, so that the tone signal G becomes richin tone color.

Similarly, a pitch of the tone signal G 1? corresponding to thekeyswitch 303 is determined by a signal G 1? derived from the signalsource 297 through a resistor 324. The signal G lt is mixed with threeadditional signals G 11, G 11 and G 11 derived from the signal sources298, 299 and 300 through resistors 323, 322 and 321, respectively, sothat the tone signal G il becomes rich in tone color.

Each of the other tone signals A A 11, B C C tt (not shown) is composedof a signal generated directly by a signal source and of severaladditional signals of signal sources, said several additional signalsbeing in octave relation to said signal generated directly by a signalsource and acting as upper harmonics of said signal generated directlyby a signal source.

Several additional signals not only modify the tone color of a tonesignal but also determine the tone color of the tone signal, becausesaid additional signals act as upper harmonics, or as upper frequencycomponents of the tone signal.

It is important that said several additional signals are mixed in eachof the tone signals. If not so, there will be conspicuous differences intone color among three kinds of tone signals, that is to say, among thefirst kind of tone signals C F 1? having perfect fourth typedifference-signals, the second kind of tone signals G F 11 havingperfect fifth type difference-signals and the third kind of tone signalsG 6 1$, A having no difference-signals.

Tone colors of the tone signals characterized by having severaladditional signals become extremely similar to each other with the helpof additional signals. Consequently, there are no conspicuousdifferences in tone color among the first kind of seven tone signals C F1? the second kind of twelve tone signals G F tt and the third kind ofthe remaining tone signals G G 1? Therefore, nineteen difference-signalsincluding two kinds of difference signals are used as tone signals ofthe manual keyboard without any hindrance for musical performance.

The concept of the novel difference signal system according to theinvention can be applied not only to the manual keyboard of anelectronic muiscal instrument, but also to the pedal keyboard of anelectronic musical instrument in such a way that the pedal keyboardcontrols tone signals completed by the novel difference signal system.

It is believed that the invention and its advantages have beenunderstood from the foregoing description and it is apparent thatvarious changes may be made in the form, construction and arrangement ofthe parts without departing from the spirit and scope of the inventionor sacrificing its advantages, the forms hereinbefore described andillustrated in the drawings being merely pre ferred embodiments thereof.

We claim:

1. An electronic musical instrument comprising in combination:

(1) a signal generating system having twelve tone series of signalsources for generating signals of pitches corresponding to the equaltempered musical scale;

(2) a keyswitch system which is coupled to said signal generating systemand which has a plurality of keyswitches capable of switching-on tonesignals corresponding to depressed keys;

(3) an output system which is coupled to said keyswitch system and whichincludes an amplifier and electro-acoustic translating means; and

(4) a difference signal system which is included in said signalgenerating system and which comprises nineteen difference-signalgenerators for producing nineteen difference-signals in a low frequencyrange in such a way that (a) each of lower seven series of said twelvetone series has a pair of difference-signal generators, one of whichproduces a difference-signal as the lowest signal of said each of lowerseven series, the other of which produces a difference-signal as thesecond lowest signal of said each of lower seven series,

(b) and that each of upper five series of said twelve tone series has asingle difference-signal generator which produces a difference-signal asthe lowest signal of said each of upper five series, each of nineteendifference-signal generators mixing two signals of signal sources, oneof which is essentially in octave relation to a difference-signal to beproduced by said each of nineteen difference-signal generators, theother of which is in non-octave relation to said difference-signal to beproduced by said each of nineteen difference-signal generators.

2. The electronic musical instrument as defined in claim 1, wherein:

said one of a pair of difference-signal generators produces adifference-signal by mixing two signals of signal sources in a pitchinterval of musical perfect fourth, said the other of a pair ofdifference-signal generators produces a difference signal by mixing twosignals of signal sources in a pitch interval of musical perfect fifth,and said single difference-signal generator produces a difference-signalby mixing two signals of signal sources in a pitch interval of musicalperfect fifth.

3. The electronic musical instrument as defined in claim 1, wherein eachof said nineteen difference-signals is mixed with a plurality ofadditional signals which are essentially in octave relation to said eachof said nineteen differencesignals and act as upper harmonics of saideach of said nineteen difference-signals.

4. The electronic musical instrument as defined in claim 3, wherein:

said plurality of additional signals include at least a plurality ofsignals of said signal sources.

5. The electronic musical instrument as defined in claim 3, wherein:

said plurality of additional signals include at least a plurality ofsignals of said signal sources and one of said nineteendifference-signals.

6. A difference-signal generator adapted for an electronic musicalinstrument of keyboard type comprising in combination:

(1) a nonlinear circuit for generating a differencesignal by mixing twosignals of pitches corresponding to the equal tempered musical scale,one of said two signals being a signal essentially in octave relation tosaid difference-signal, the other of said two signals being a signal innon-octave relation to said difference-signal,

(2) a low pass filter for weakening said differencesignal in theovertone frequency components thereof, and

(3) means for mixing the weakened difference-signal with said signalessentially in octave relation to said diiference-signal.

7. The diiference-signal generator as defined in claim 6, wherein saidtwo signals are in a pitch interval of musical perfect fifth, said oneof said two signals being a signal in an exact frequency 2n Hz., saidthe other of said two signals being a signal in a slightly deviatedfrequency 3n Hz.

8. The difference-signal generator as defined in claim 6, wherein saidtwo signals are in a pitch interval of musical perfect fourth, said oneof said two signals being a signal in an exact frequency 4n Hz., saidthe other of two signals being a signal in a slightly deviated frequency3n Hz.

9. A difference-signal generator adapted for an electronic musicalinstrument of keyboard type comprising in combination:

(1) a low pass filter for weakening the overtone frequency component ofa signal which is in non-octave relation to a difference-signal to beproduced by said difference-signal generator, and

(2) means for mixing said weakened signal in nonoctave relation to saiddifference-signal with a signal essentially in octave relation to saiddifference-signal,

(a) said signal in non-octave relation to said difference-signal andsaid signal essentially in octave relation to said difference-signalhaving pitches corresponding to the equal tempered musical scale.

10. The difference-signal generator as defined in claim 9, wherein saidsignal in non-octave relation to said difference-signal and said signalessentially in octave relation to said difference-signal are in a pitchinterval of musical perfect fifth, said signal in non-octave relation tosaid difference-signal being a signal in a slightly deviated frequency3n Hz., said signal essentially in octave relation to saiddifference-signal being a signal in an exact frequency 211 Hz.

11. The difference-signal generator as defined in claim 9, wherein saidsignal in non-octave relation to said difference-signal and said signalessentially in octave relation to said difference-signal are in a pitchinterval of musical perfect fourth, said signal in non-octave relationto said diiference-signal being a signal in a slightly deviatedfrequency 3n Hz., said signal essentially in octave relation to saiddiiference-signal being a signal in an exact frequency 4n Hz.

References Cited UNITED STATES PATENTS 2,045,172 6/1936 Yungblut 841.172,142,580 1/1939 Williams 84--1.23 X 2,533,821 12/1950 Langer 841.192,557,133 6/1951 Mork 84-1.17 2,571,141 10/1951 Knoblaugh 61 al. s4-1.1s 2,971,420 2/1961 Anderson s4 1.22

FOREIGN PATENTS 1,109,696 1/1956 France.

HERMAN KARL SAALBACH, Primary Examiner TIM VEZEAU, Assistant ExaminerU.S. Cl. X.R. 84-1.17, 1.22 r

